1. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 1 1 Chapter 8 Memory Testing and Built-In Self-Test

2. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 2 2 What is this chapter about?  Basic concepts of memory testing and BIST  Memory fault models and test algorithms  Memory fault simulation and test algorithm generation  RAMSES: fault simulator  TAGS: test algorithm generator  Memory BIST  BRAINS: BIST generator

3. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 3 3 Typical RAM Production Flow Wafer Full Probe TestMarking Final Test Shipping QA Sample Test Visual Inspection Burn-In (BI) Post-BI TestLaser RepairPackaging Pre-BI Test

4. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 4 4 Off-Line Testing of RAM  Parametric Test: DC & AC  Reliability Screening  Long-cycle testing  Burn-in: static & dynamic BI  Functional Test  Device characterization –Failure analysis  Fault modeling –Simple but effective (accurate & realistic?)  Test algorithm generation –Small number of test patterns (data backgrounds) –High fault coverage –Short test time

5. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 5 5 DRAM Functional Model

6. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 6 6 DRAM Functional Model Example

7. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 7 7 Functional Fault Models  Classical fault models are not sufficient to represent all important failure modes in RAM.  Sequential ATPG is not possible for RAM.  Functional fault models are commonly used for memories:  They define functional behavior of faulty memories.  New fault models are being proposed to cover new defects and failures in modern memories:  New process technologies  New devices

8. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 8 8 Static RAM Fault Models: SAF/TF  Stuck-At Fault (SAF)  Cell (line) SA0 or SA1 –A stuck-at fault (SAF) occurs when the value of a cell or line is always 0 (a stuck-at-0 fault) or always 1 (a stuck- at-1 fault). –A test that detects all SAFs guarantees that from each cell, a 0 and a 1 must be read.  Transition Fault (TF)  Cell fails to transit from 0 to 1 or 1 to 0 in specified time period. –A cell has a transition fault (TF) if it fails to transit from 0 to 1 (a TF) or from 1 to 0 (a TF).

9. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 9 9 Static RAM Fault Models: AF  Address-Decoder Fault (AF)  An address decoder fault (AF) is a functional fault in the address decoder that results in one of four kinds of abnormal behavior: –Given a certain address, no cell will be accessed –A certain cell is never accessed by any address –Given a certain address, multiple cells are accessed –A certain cell can be accessed by multiple addresses

10. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 10 10 Static RAM Fault Models: SOF  Stuck-Open Fault (SOF)  A stuck-open fault (SOF) occurs when the cell cannot be accessed due to, e.g., a broken word line.  A read to this cell will produce the previously read value.

11. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 11 11 RAM Fault Models: CF  Coupling Fault (CF)  A coupling fault (CF) between two cells occurs when the logic value of a cell is influenced by the content of, or operation on, another cell.  State Coupling Fault (CFst) –Coupled (victim) cell is forced to 0 or 1 if coupling (aggressor) cell is in given state.  Inversion Coupling Fault (CFin) –Transition in coupling cell complements (inverts) coupled cell.  Idempotent Coupling Fault (CFid) –Coupled cell is forced to 0 or 1 if coupling cell transits from 0 to 1 or 1 to 0.

12. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 12 12 Intra-Word & Inter-Word CFs

13. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 13 13 RAM Fault Models: DF  Disturb Fault (DF)  Victim cell forced to 0 or 1 if we (successively) read or write aggressor cell (may be the same cell): –Hammer test  Read Disturb Fault (RDF) –There is a read disturb fault (RDF) if the cell value will flip when being read (successively).

14. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 14 14 RAM Fault Models: DRF  Data Retention Fault (DRF)  DRAM –Refresh Fault –Leakage Fault  SRAM –Leakage Fault l Static Data Losses---defective pull-up

15. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 15 15 Test Time Complexity (100MHz)

16. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 16 16 RAM Test Algorithm  A test algorithm (or simply test) is a finite sequence of test elements:  A test element contains a number of memory operations (access commands) –Data pattern (background) specified for the Read and Write operation –Address (sequence) specified for the Read and Write operations  A march test algorithm is a finite sequence of march elements:  A march element is specified by an address order and a finite number of Read/Write operations

17. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 17 17 March Test Notation   : address sequence is in the ascending order   : address changes in the descending order   : address sequence is either  or   r: the Read operation  Reading an expected 0 from a cell (r0); reading an expected 1 from a cell (r1)  w: the Write operation  Writing a 0 into a cell (w0); writing a 1 into a cell (w1)  Example (MATS+):

18. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 18 18 Classical Test Algorithms: MSCAN  Zero-One Algorithm [Breuer & Friedman 1976]  Also known as MSCAN  SAF is detected if the address decoder is correct (not all AFs are covered): –Theorem: A test detects all AFs if it contains the march elements  (ra,…,wb) and  (rb,…,wa), and the memory is initialized to the proper value before each march element  Solid background (pattern)  Complexity is 4N

19. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 19 19 Classical Test Algorithms: Checkerboard  Checkerboard Algorithm  Zero-one algorithm with checkerboard pattern  Complexity is 4N  Must create true physical checkerboard, not logical checkerboard  For SAF, DRF, shorts between cells, and half of the TFs –Not good for AFs, and some CFs cannot be detected

20. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 20 20 Classical Test Algorithms: GALPAT  Galloping Pattern (GALPAT)  Complexity is 4N**2─only for characterization  A strong test for most faults: all AFs, TFs, CFs, and SAFs are detected and located 1. Write background 0; 2. For BC = 0 to N-1 { Complement BC; For OC = 0 to N-1, OC != BC; { Read BC; Read OC; } Complement BC; } 3. Write background 1; 4. Repeat Step 2;

21. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 21 21 Classical Test Algorithms: WALPAT  Walking Pattern (WALPAT)  Similar to GALPAT, except that BC is read only after all others are read.  Complexity is 2N**2.

22. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 22 22 Classical Test Algorithms: Sliding  Sliding (Galloping) Row/Column/Diagonal  Based on GALPAT, but instead of shifting a 1 through the memory, a complete diagonal of 1s is shifted: –The whole memory is read after each shift  Detects all faults as GALPAT, except for some CFs  Complexity is 4N**1.5.

23. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 23 23 Classical Test Algorithms: Butterfly  Butterfly Algorithm  Complexity is 5NlogN  All SAFs and some AFs are detected 1. Write background 0; 2. For BC = 0 to N-1 { Complement BC; dist = 1; While dist <= mdist /* mdist < 0.5 col/row length */ { Read cell @ dist north from BC; Read cell @ dist east from BC; Read cell @ dist south from BC; Read cell @ dist west from BC; Read BC; dist *= 2; } Complement BC; } 3. Write background 1; repeat Step 2;

24. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 24 24 Classical Test Algorithms: MOVI  Moving Inversion (MOVI) Algorithm  For functional and AC parametric test –Functional (13N): for AF, SAF, TF, and most CF –Parametric (12NlogN): for Read access time l 2 successive Reads @ 2 different addresses with different data for all 2-address sequences differing in 1 bit l Repeat T2~T5 for each address bit l GALPAT---all 2-address sequences

25. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 25 25 Classical Test Algorithms: SD  Surround Disturb Algorithm  Examine how the cells in a row are affected when complementary data are written into adjacent cells of neighboring rows.  Designed on the premise that DRAM cells are most susceptible to interference from their nearest neighbors (eliminates global sensitivity checks). 1. For each cell[p,q] /* row p and column q */ { Write 0 in cell[p,q-1]; Write 0 in cell[p,q]; Write 0 in cell[p,q+1]; Write 1 in cell[p-1,q]; Read 0 from cell[p,q+1]; Write 1 in cell[p+1,q]; Read 0 from cell[p,q-1]; Read 0 from cell[p,q]; } 2. Repeat Step 1 with complementary data; 1 000 1

26. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 26 26 Simple March Tests  Zero-One (MSCAN)  Modified Algorithmic Test Sequence (MATS)  OR-type address decoder fault  AND-type address decoder fault  MATS+  For both OR- & AND-type AFs and SAFs  The suggested test for unlinked SAFs

27. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 27 27 March Tests: Marching-1/0  Marching-1/0  Marching-1: begins by writing a background of 0s, then read and write back complement values (and read again to verify) for all cells (from cell 0 to n-1, and then from cell n-1 to 0), in 7N time  Marching-0: follows exactly the same pattern, with the data reversed  For AF, SAF, and TF (but only part of the CFs)  It is a complete test, i.e., all faults that should be detected are covered  It however is a redundant test, because only the first three march elements are necessary

28. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 28 28 March Tests: MATS++  MATS++  Also for AF, SAF, and TF  Optimized marching-1/0 scheme—complete and irredundant  Similar to MATS+, but allow for the coverage of TFs  The suggested test for unlinked SAFs & TFs

29. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 29 29 March Tests: March X/C  March X  Called March X because the test has been used without being published  For AF, SAF, TF, & CFin  March C  For AF, SAF, TF, & all CFs, but semi-optimal (redundant)

30. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 30 30 March Tests: March C-  March C-  Remove the redundancy in March C  Also for AF, SAF, TF, & all CFs  Optimal (irredundant)  Extended March C-  Covers SOF in addition to the above faults

31. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 31 31 Fault Detection Summary

32. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 32 32 Comparison of March Tests

33. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 33 33 Word-Oriented Memory  A word-oriented memory has Read/Write operations that access the memory cell array by a word instead of a bit.  Word-oriented memories can be tested by applying a bit-oriented test algorithm repeatedly with a set of different data backgrounds:  The repeating procedure multiplies the testing time

34. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 34 34 Testing Word-Oriented RAM  Background bit is replaced by background word  MATS++:  Conventional method is to use logm+1 different backgrounds for m-bit words  Called standard backgrounds  m=8: 00000000, 01010101, 00110011, and 00001111  Apply the test algorithm logm+1=4 times, so complexity is 4*6N/8=3N Note: b is the complement of a

35. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 35 35 Cocktail-March Algorithms  Motivation:  Repeating the same algorithm for all logm+1 backgrounds is redundant so far as intra-word coupling faults are concerned  Different algorithms target different faults.  Approaches: 1.Use multiple backgrounds in a single algorithm run 2.Merge and forge different algorithms and backgrounds into a single algorithm  Good for word-oriented memories Ref: Wu et al., IEEE TCAD, 04/02

36. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 36 36 March-CW  Algorithm:  March C- for solid background (0000)  Then a 5N March for each of other standard backgrounds (0101, 0011):  Results:  Complexity is (10+5logm)N, where m is word length and N is word count  Test time is reduced by 39% if m=4, as compared with extended March C-  Improvement increases as m increases Ref: Wu et al., IEEE TCAD, 04/02

37. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 37 37 Multi-Port Memory Fault Models  Cell Faults:  Single cell faults: SAF, TF, RDF  Two-cell coupling faults –Inversion coupling fault (CFin) –State coupling fault (CFst) –Idempotent coupling fault (CFid)  Port Faults:  Stuck-open fault (SOF)  Address decoder fault (AF)  Multi-port fault (MPF)

38. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 38 38 2-Port RAM Topology

39. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 39 39 Inter-Port Word-Line Short * Functional test complexity: O(N 3 )

40. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 40 40 Inter-Port Bit-Line Short * Functional test complexity: O(N 2 )

41. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 41 41 Why Memory Fault Simulation?  Fault coverage evaluation can be done efficiently, especially when the number of fault models is large.  In addition to bit-oriented memories, word- oriented memories can be simulated easily even with multiple backgrounds.  Test algorithm design and optimization can be done in a much easier way.  Detection of a test algorithm on unexpected faults can be discovered.  Fault dictionary can be constructed for easy diagnosis.

42. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 42 42 Sequential Memory Fault Simulation  Complexity is N**3 for 2-cell CF For each fault /* N**2 for 2-cell CF */ Inject fault; For each test element /* N for March */ { Apply test element; Report error output; }

43. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 43 43 Parallel Fault Simulation  RAMSES [Wu, Huang, & Wu, DFT99 & IEEE TCAD 4/02]  Each fault model has a fault descriptor # S/1 AGR := w0 SPT := @ /* Single-cell fault */ VTM := r0 RCV := w1 # CFst AGR := v0 SPT := */* All other cells are suspects */ VTM := r0 RCV := w1

44. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 44 44 RAMSES  Complexity is N**2 For each test operation { If op is AGR then mark victim cells; If op is RCV then release victim cells; If op is VTM then report error; }

45. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 45 45 RAMSES Algorithm

46. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 46 46 RAMSES Example for CFin RAMSES Example for CFin

47. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 47 47 Coverage of March Tests ☞ Extended March C- has 100% coverage of SOF

48. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 48 48 Test Algorithm Generation Goals  Given a set of target fault models, generate a test with 100% fault coverage  Given a set of target fault models and a test length constraint, generate a test with the highest fault coverage  Priority setting for fault models  Test length/test time can be reduced  Diagnostic test generation  Need longer test to distinguish faults

49. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 49 49 Test Algorithm Generation by Simulation (TAGS)  March template abstraction : ↑(w0); ↑(r0,w1); ↓(r1,w0,r0) ↑(w) ↑(r,w); ↓(r,w,r) (w)(rw)(rwr)

50. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 50 50 Template Set  Exhaustive generation: complexity is very high, e.g., 6.7 million templates when N = 9  Heuristics should be developed to select useful templates T(1N) (w) T(2N) (ww)(w)(r)(wr)(w)(w) T(3N) (www)(ww)(w)(w)(ww) (wwr)(wrw)(wr)(w) …. (w)(rw)

51. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 51 51 TAGS Procedure 1. Initialize test length as 1N, T(1N) = {(w)}; 2. Increase test length by 1N: apply generation options; 3. Apply filter options; 4. Assign address orders and data backgrounds; 5. Fault simulation using RAMSES; 6. Drop ineffective tests; 7. Repeat 2-6 using the new template set until constraints met;

52. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 52 52 Template Generation/Filtering  Generation heuristics:  (r) insertion  (…r), (r…) expansion  (w) insertion  (…w), (w…) expansion  Filtering heuristics:  Consecutive read: (…rr…)  Repeated read: (r)(r)  Tailing single write: …(w)

53. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 53 53 TAGS Example (1/2)  Target fault models (SAF, TF, AF, SOF, Cfin, Cfid, CFst), time constraints ∞:

54. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 54 54 TAGS Example (2/2)

55. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 55 55 RAMSES Simulation Results

56. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 56 56 FC Spectrum for 6 N Tests

57. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 57 57 Word-Oriented TAGS 1. Construct bit-oriented test algorithms 2. Generate initial Cocktail-March: Assign each data background to the test in Step 1─a cascade of multiple March algorithms 3. Optimize the Cocktail-March (!P 1 ) /* non-solid backgrounds */ 4. Optimize the Cocktail-March (P 1 ) /* solid background */

58. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 58 58 3. Cocktail March Optimization (!P 1 ) For each non-solid data background P (P != P 1 ) a) Generate a new Cocktail–March test by replacing the March algorithm having P as its background with a shorter one from the set of algorithms generated in Step 1. b) Run RAMSES for the new Cocktail–March. c) Repeat 3(a) and 3(b) until the FC drops and cannot be recovered by any other test algorithm of the same length. d) Store the test algorithm candidates used in the previous step.

59. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 59 59 4. Cocktail March Optimization (P 1 ) a) Generate a new Cocktail–March test by replacing the March algorithm having P 1 as its background with a shorter one from the test set generated in Step 1. Repeat with every test candidate for other backgrounds. b) Run RAMSES for the new Cocktail–March. c) Repeat 4(a) and 4(b) for all candidate test algorithms from 3(d) until the FC drops and cannot be recovered by any other test algorithm of the same length or by selecting other candidates.

60. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 60 60 Cocktail March Example (m=8) Ref: Wu et al., IEEE TCAD, 4/02

61. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 61 61 What Can BIST do?  What are the functional faults to be covered?  Static and dynamic  Operation modes  What are the defects to be covered?  Opens, shorts, timing parameters, voltages, currents, etc.  Can it support fault location and redundancy repair?  Can it support BI?  Can it support on-chip redundancy analysis and repair?  Does it allow characterization test as well as mass production test?  Can it really replace ATE (and laser repair machine)?  Programmability, speed, timing accuracy, threshold range, parallelism, etc.

62. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 62 62 Typical RAM BIST Approaches  Methodology  Processor-based BIST –Programmable  Hardwired BIST –Fast –Compact  Hybrid  Interface  Serial (scan, 1149.1)  Parallel (embedded controller; hierarchical)  Patterns (address sequence)  March & March-like  Pseudorandom  Others

63. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 63 63 Typical RAM BIST Architecture RAM Test Collar (MUX) BIST Module Controller Comparator Pattern Generator Go/No-Go RAM Controller

64. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 64 64 EDO DRAM BIST Example

65. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 65 65 DRAM Page-Mode Read-Write Cycle

66. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 66 66 BIST Architecture

67. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 67 67 BIST External I/O  MBS (Memory BIST Selection): controller test collar (normal/test mode selection)  MBC (Memory BIST Control): Controller input  MCK (Memory BIST Clock)  MBR (Memory BIST Reset)  MSI (Memory BIST Scan In): for test commands and scan test inputs  MSO (Memory BIST Scan Out): for diagnostic data and scan test outputs  MBO (Memory BIST Output): error indicator  MRD (Memory BIST Output Ready): BIST completion flag

68. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 68 68 BIST I/O Summary

69. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 69 69 Controller and Sequencer  Controller  Microprogram  Hardwired  Shared CPU core  IEEE 1149.1 TAP  PLD  Sequencer (Pattern Generator)  Counter  LFSR  LUT  PLD

70. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 70 70Controller

71. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 71 71 Sequencer

72. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 72 72 Sequencer States

73. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 73 73 BIST Test Modes 1. Scan-Test Mode 2. RAM-BIST Mode 1.Functional faults 2.Timing faults (setup/hold times, rise/fall times, etc.) 3.Data retention faults 3. RAM-Diagnosis Mode 4. RAM-BI Mode

74. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 74 74 BIST Controller Commands

75. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 75 75 BIST Control Sequence

76. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 76 76 RAM BIST Compiler  Use of RAM cores is increasing  SRAM, DRAM, flash RAM  Multiple cores  RAM BIST compiler is the trend  BRAINS (BIST for RAM in Seconds)  Proposed BIST Architecture  Memory Modeling  Command Sequence Generation  Configuration of the Proposed BIST

77. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 77 77 BRAINS Output Specification  Synthesizable BIST design  At-speed testing  Programmable March algorithms  Optional diagnosis support –BISD  Activation sequence  Test bench  Synthesis script

78. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 78 78 BRAINS Inputs and Outputs

79. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 79 79 General RAM BIST Architecture

80. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 80 80 Sequencer Block Diagram Control Module Control Module Address Generator Sequence Generator Command Generator Error Handling Module address command error info. go error signature en done March element go

81. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 81 81 Function of the TPG  The test pattern generator (TPG) translates high-level memory commands to memory input signals.  Four parameters to model a memory’s I/Os:  Type: input, output, and in/out  Width  Latency: number of clock cycles the TPG generates the physical signal after it receives a command from the sequencer  Packet_length: number of different signal values packed within a single clock cycle BIST Controller Sequencer TPGRAM

82. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 82 82 Architecture of the TPG

83. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 83 83 Multiple RAM Cores  Controller and sequencer can be shared controller Test pattern generator Test pattern generator sequencer Ram Core A Ram Core B Ram Core C Test pattern generator sequencer

84. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 84 84 Sharing Controller & Sequencer

85. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 85 85 Grouping and Scheduling

86. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 86 86 BRAINS BIST Architecture MBSMSIMBOMRDMSOMBCMBRMCK Sequencer TPG RAM Memory BIST External Tester Controller RAM Source: ATS’01

87. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 87 87 BRAINS GUI

88. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 88 88 Supported Memories  The Built-In Memory List  DRAM –EDO DRAM –SDRAM –DDR SDRAM  SRAM –Single-Port Synchronous SRAM –Single-Port Asynchronous SRAM –Two-Port Synchronous Register File –Dual-Port Synchronous SRAM –Micron ZBT SRAM  BRAINS can support new memory architectures easily

89. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 89 89 Examples

90. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 90 90 Area Overhead

91. EE141 VLSI Test Principles and Architectures Ch. 8 - Memory Testing & BIST - P. 91 91 Concluding Remarks  BIST is considered the best solution for testing embedded memories:  Low cost  Effective and efficient  Further improvement can be expected to extend the scope of RAM BIST:  Timing/delay faults and disturb faults  BISD and BISR  CAM BIST and flash BIST  BIST/BISD/BISR compiler  Wafer-level BI and test –Known good die